The invention relates to a crankshaft for a reciprocating piston engine.
It is known from the prior art that crankshafts of reciprocating piston engines are exposed to high torsional moments, and also to many load changes and consequently must have a particularly high resistance to load changes. The conventional methods for production of crankshafts include both forging and also casting processes, wherein first of all the particular crankshaft is produced in its rough state and subsequently the crankshaft undergoes the appropriate final processing steps to meet the respective requirements. These final processing steps include for example balancing of the crankshaft for elimination of rotational irregularities, or the surface processing of respective journals which correspond to respective bearings of the engine or respective big end bearings. In addition to the surface processing of corresponding bearing points of the crankshaft, the final processing also includes the reduction of stress peaks, such as are produced as a consequence of bending or torsional stress on the crankshaft.
It is known from DE 24 35 476 A1 that barrel-shaped hollow bores in the corresponding crank pins of the crankshaft lead to a more favorable stress distribution in the crankshaft. Consequently, the stress peaks are reduced and the stress distribution in the crankshaft takes place in a more uniform manner.
From JP 2000 320531 A a crankshaft of an internal combustion engine is known which comprises an accumulation of material on the ground pin side facing away from a crank arm in the rotation axis. This accumulation of material is used to improve the stiffness of the crankshaft combined with low weight gain. The crankshaft shown has no through hole.
From JP S55 37276 A a crankshaft is known, which has an accumulation of material on a crank arm for reasons of machining of the groove and an axial thrust surface.
In this connection it is usual for at least most of the crank pins, which are also designated as shaft journals, to have a bore drilled through them along the axis of rotation of the crankshaft in order to achieve the most uniform stress distribution possible along the entire crankshaft. Furthermore, it is known that the length of the crankshaft increases with the number of cylinders of the reciprocating piston engine. In order to ensure that the bores in the respective shaft journal of the crankshaft are particularly accurately aligned with one another, it is necessary to produce these bores in the context of one individual working step. Thus, in other words, the drilling tool is set on an end of the crankshaft on the longitudinal axis which corresponds to the axis of rotation of the crankshaft, and the shaft journals of the crankshaft have a bore drilled through them along this axis of rotation in one working step. However, this working step is subject to a particularly difficult process management, as a particularly long drilling tool which produces the corresponding bores in the shaft journals particularly centrally and accordingly with a particularly small axial offset with respect to one another is necessary for the drilling of the bore through the crankshaft in the context of an individual working step.
The object of the present invention is to create a crankshaft for a reciprocating piston engine in which the corresponding shaft journals have bores aligned particularly accurately with one another.
In order to create a crankshaft of the type referred to above which has bores aligned particularly accurately with one another in the respective shaft journals in the form of a through bore relating to the respective shaft journal, according to the invention it is provided that respective material accumulations, which in each case have a surface oriented at least substantially orthogonally with respect to the axis of rotation, are provided on the crank webs in the region of an axis of rotation. Consequently, according to the invention, it is provided that, by means of these material accumulations, respective surfaces on the crank webs of the crankshaft, on which the drill enters or exits the material of the crankshaft in a perpendicular manner, are created for the drilling tool. As a result, the lateral forces on the drilling tool are reduced to a minimum when the tool penetrates into the material of the crankshaft or exits from the material of the crankshaft. Thus, it is ensured that the drilling tool does not impinge on an oblique surface which can lead to drifting of the drilling tool and consequently to a bore with less precision. In this connection it is particularly advantageous if the crankshaft already has these material accumulations in its rough state, that is to say before any final processing steps such as for example the surface processing of the respective shaft journals or crank pins has been carried out. Consequently, it is particularly favorable if already at the time of production of the crankshaft, that is to say for example at the time of forging or casting the crankshaft, these material accumulations are attached to the crankshaft, that is to say they are produced in one piece with the crankshaft.
Thus, due to the material accumulations, no guide means such as for example sleeves for guiding the drill between the individual drill entries and exits are necessary. Thus, in other words, the guiding of the drilling tool is performed merely by the crankshaft itself through which the bore is to be drilled. By the prevention of transverse forces and sliding of the drill during the drilling operation, such as would be the case in the event of the drill tip striking an oblique surface, on the one hand the through bore is produced particularly precisely and, on the other hand, the service life of the drilling tool is significantly increased.
Further advantages, features and details of the invention can be seen from the following description of a preferred exemplary embodiment and with reference to the drawings.